Fix clang resource directory path

The clang resource directory is always in lib/, while this was
creating the directories in lib64 (for 64-bit symbols).

This should fix the following error on ppc64le:

> error: Directory not found: /builddir/build/BUILDROOT/llvm-19.0.0~pre20240528.g1de1ee9cbabd64-1.fc39.ppc64le/usr/lib/clang/19/bin

Author: nikic

install.spec.inc

@@ -182,7 +182,7 @@ chmod u-x %{buildroot}%{_mandir}/man1/scan-build.1*
 
 # Create sub-directories in the clang resource directory that will be
 # populated by other packages
-mkdir -p %{buildroot}%{install_libdir}/clang/%{maj_ver}/{bin,include,lib,share}/
+mkdir -p %{buildroot}%{_prefix}/lib/clang/%{maj_ver}/{bin,include,lib,share}/
 
 %if %{without compat_build}
 # Add a symlink in /usr/bin to clang-format-diff